Tenoumer impact crater,Mauritania: Impact melt genesis from a lithologically diverse target

Impact melt rocks from the 1.9 km diameter, simple bowl‐shaped Tenoumer impact crater in Mauritania have been analyzed chemically and petrologically. They are heterogeneous and can be subdivided into three types based on melt matrix color, occurrence of lithic clast components, amount of vesiculation (melt degassing), different proportions of carbonate melt mingled into silicate melt, and bulk rock chemical composition. These heterogeneities have two main causes (1) due to the small size of the impact crater, there was probably no coherent melt pool where a homogeneous mixture of melts, derived from different target lithologies, could be created; and (2) melt rock heterogeneity occurring at the thin section scale is due to fast cooling during and after the dynamic ejection and emplacement process. The overall period of crystal growth from these diverse melts was extremely short, which provides a further indication that complete chemical equilibration of the phases could not be achieved in such short time. Melt mixing processes involved in the generation of impact melts are, thus, recorded in nonequilibrium growth features. Variable mixing processes between chemically different melt phases and the formation of hybrid melts can be observed even at millimeter scales. Due to extreme cooling rates, different mixing and mingling stages are preserved in the varied parageneses of matrix minerals and in the mineral chemistry of microlites. ⁴⁰Ar³⁹Ar step‐heating chronology on specimens from three melt rock samples yielded five concordant inverse isochron ages. The inverse isochron plots show that minute amounts of inherited ⁴⁰Ar* are present in the system. We calculated a weighted mean age of 1.57 ± 0.14 Ma for these new results. This preferred age represents a refinement from the previous range of 21 ka to 2.5 Ma ages based on K/Ar and fission track dating.     

Tracing salinization processes in coastal aquifers using an isotopic and geochemical approach: comparative studies in western Morocco and southwest Portugal

Environmental stable and radioactive isotopes (δ²H, δ¹³C, δ¹⁸O; ³H and ¹⁴C), together with physical and geochemical data, were used in the determination of the origins of groundwater salinization and geochemical evolution processes in coastal regions. Two case studies on the Atlantic Coast are discussed, one located in the Essaouira sedimentary basin, western Morocco, and the second, in the Lower Tagus–Sado sedimentary basin, southwest Portugal. In both regions, groundwater degradation occurs by salinization increase to different concentrations and in relation to different origins. The main quality issues for the groundwater resources are related to seawater intrusion, dissolution of diapiric structures intruding the aquifer layers, brine dissolution at depth, and/or evaporation of irrigation water. Anthropogenic pollution ascribed to agricultural activities is another source for groundwater degradation, affecting mainly the shallow aquifers. The apparent ¹⁴C age of the analysed samples ranges from 2.9?±?0.3 up to 45.6?±?0.6 pmC in the Miocene groundwater samples from the basin in Portugal; at the Essaouira basin in Morocco, the ¹⁴C content varies from 60 to 86 pmC. In most of the water samples, the ³H concentration is below the detection limit. In both basins, the isotopic results together with the geochemical data provided an effective label for tracing the mineralization origin and groundwater degradation processes. Further, the isotopic signatures were used in the identification of a paleoclimate (colder period), recorded in the stable isotopic composition and corroborated with the ¹⁴C data.     

Combined modeling of thermal evolution and accretion of trans-neptunian objects—Occurrence of high temperatures and liquid water

We have calculated the early thermal evolution of trans-neptunian objects by means of a thermal evolution code that takes into account simultaneous accretion. The set of coupled partial differential equations for ²⁶Al radioactive heating, transformation of amorphous to crystalline ice and melting of water ice was solved numerically for small porous icy (cometary-like) bodies growing to final radii between 2 and 32 km and accreting between 20 and 44 AU. Accretion within a swarm of gravitationally interacting small bodies was calculated self-consistently with a simple accretion algorithm and thermal evolution of a typical member of the swarm was tracked in a parameter-space survey. We find that including accretion in numerical modeling of thermal evolution leads to a broad variety of thermally processed icy bodies and that the early occurrence of liquid water and extended crystalline ice interiors may be a very common phenomenon. The pristine nature of small icy bodies becomes thus restricted to a particular set of initial conditions. Generally, long-period comets should be more thermally affected than short-period ones.     

Valorization of Agricultural By-Products Within the “Energyscapes”: Renewable Energy as Driving Force in Modeling Rural Landscape

Due to several growing environmental constraints, renewable energy sources currently play an increasingly crucial role that, owing to their high temporal and spatial variability, needs a careful planning approach. It is important therefore to develop a framework that examines the distribution of different energy sources in a spatio-temporal context. From an energy point of view, a regional territory, such as an internal southern Italian region (the Basilicata Region), can be considered as a paradigmatic case study, because it is characterized by significant sources of renewable energy (e.g., biomass, wind, solar, hydro) connected to its morphological and environmental structure, as well as to its agricultural and food productions. The present paper in based on an analysis of the spatial supply and relationships between renewable energy potentials and rural land, through the use of a Geographic Information System that has been implemented with the aim to analyze the energy system, as well as to optimize the valorization of biomass resources that may be still unutilized within the bioenergy production chain. This study has been carried out even to bridge the gap between energy systems modeling and landscape planning. Within this context, an “Energyscape” may be considered as the effect resulting on the rural landscape from a combination of the supply, demand and infrastructure for energy. This framework could be therefore a starting point for an interdisciplinary analysis able to figure out optimal solutions in decision-making processes, which duly respect the protection and restoring of endangered ecosystems, supporting the decision about an optimal spatial localization of energy plants as well.

     

The KS-transformation in hypercomplex form and the quantization of the negative-energy orbit manifold of the Kepler problem

In a previous note we have shown that the KS-transformation, introduced by Kustaanheimo and Stiefel into Celestial Mechanics for the regularization of the Kepler problem, may be formulated in terms of hypercomplex numbers as the product of a quaternion and its anti-involute, thus representing a particular morphism of the real algebra of quaternions-having for image the physical configuration space of the Kepler problem. In the present note we show, first, that this formulation allows a straight derivation of the Hopf fibering of the sphere S³ (characterized by unit quaternions) having the base space given by the sphere S² (characterized by unit vectors), and secondly that the KS-transformation allows the quantization of the symplectic manifold S² in the sense of Souriau, the associated quantum manifold S³ having a contact structure given by the bilinear relation characteristic of the KS-theory. Furthermore, after presenting a natural extension of the hypercomplex KS-transformation to the full phase space of the Kepler problem, we show that this extension allows the quantization of the manifold of Kepler orbits of fixed negative energy (manifold diffeomorphic to the symplectic product S²×S²). The energy levels satisfy a well known quantum integrality condition and the associated quantum manifold is diffeomorphic to the product manifold S³×S³ quotiented by a suitable equivalence relation.Research supported by the Consiglio Nazionale delle Ricerche of Italy, Gruppo per la Fisica-Matematica.     

Geometrical and physical outlook on the cross product of two quaternions

As an outcome of our previous notes [13, 14] on the quaternion regularization of the classical Kepler problem and pre-quantization of the Kepler manifold we show, first, that both the cross product of two quaternions and the cross product of their anti-involutes are susceptible of a simple geometrical representation in the ordinary 3-dimensional euclidean spaceR ³ and, secondly, that they satisfy anSO(4)-invariant relation that implies projection of curves from the quaternion space onto the spaceR ³. ThisSO(4)-invariance allows—in the particular case of orthogonal quaternions of equal norm—a straight derivation: (i) of the correspondence between the free motion on the surface of a sphereS ³ and the physical elliptical Kepler motion (collisions included) on a plane denoted by _w ; (ii) of the celebrated Kepler equation and (iii) of the Levi-Civita regularizing time transformation. With (i) and (ii) we recover some of Györgyi's [3] results. The aforesaid orbital plane _w and the orbital plane _*, arrived at independently by exploiting the Kustaanheimo-Stiefel regularizing transformation, are shown to be inclined exactly at an angle characterizing the ratio of the semi-axes of the elliptical orbits and intimately related to the cross product representation. Thus the eventual superimposition of the two planes confirms the intimate connection between the various regularization procedures—transforming the classical Kepler problem into the geodesic flow onS ³—and the Fock's procedure for the quantum theoretical Kepler problem of the hydrogen atom (accidental degeneracy).This research was supported by the Consiglio Nazionale delle Ricerche of Italy (C.N.R.-G.N.F.M.).     

Development of spinor descriptions of rotational mechanics from Euler's rigid body displacement theorem

Let us consider a three-body system with three given pointmasses and let us analyze its bounded solutions with a given angular momentum.Among these bounded solutions we found the three usual families of elliptic Euler solutions, with collinear central configurations, and a beautiful result would have been the following: The greatest lower bound of the moment of inertia (with respect to the center of masses) for these elliptic Euler solutions is also the greatest lower bound for all bounded solutions of the same masses and angular momentum.With the help of a new efficient test of escape we found that the greatest lower bound is always at least 99.9% of the above desired value and we think that the above conjecture is always true.This new test also leads to many adjacent results and especially, for the present, to the smallest delimitation of the zone of bounded motions.As other tests ours uses the Jacobi decomposition of the three-body motion with r being the mutual distance of the two masses of the binary and R the distance between the center of mass of the binary and the third mass.The study is divided into two parts. In the first we analyze the motion of the third mass, its acceleration and its escape velocities when, with a suitable scalar k, a condition of the type rkR remains forever satisfied. In the second part we will look for initial conditions under which the inequality rkR will remain forever satisfied and we will develop the corresponding test and its applications.     

Petrology and Fe–Ti oxide reequilibration of the 1991 Mount Unzen mixed magma

A dacitic magma (64.5 wt.% SiO₂), a mixture of phenocryst-rich rhyodacite and an aphyric mafic magma, was erupted during the recent 1991–1995 Mount Unzen eruptive cycle. The experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas, and the nature of the mixing process. The preeruption rhyodacitic magma was at a temperature of 790±20°C according to Fe–Ti oxide phenocryst cores, and at a depth of 6 to 7 km (160 MPa) according to Al-in-hornblende geobarometry. The mafic magma that mixed with the rhyodacite is found as andesitic (54 to 62 wt.% SiO₂) enclaves in the erupted magma and was essentially aphyric when intruded. Phase equilibria indicate that an aphyric andesite at 160 MPa is >1030°C (H₂O-saturated) and possibly as high as 1130°C (2 wt.% H₂O). The composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt.% SiO₂. Using these compositions and temperatures, the temperature of the Unzen magma after mixing is estimated to be at least 850° to 870°C. The groundmass Fe–Ti oxide microphenocrysts and those in pargasite-bearing reaction zones around biotite phenocrysts both give 890±20°C temperatures; the oxide–oxide contacts give temperatures of 910±20°C. The 900±30°C postmixing temperatures are consistent with phase-equilibria experiments which show that the magma was not above 930°C at 160 MPa. Our Fe–Ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption, which is a shorter time than is calculated using available diffusion data. There is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma.     

Carbon Dioxide Discharged through the Las Cañadas Aquifer, Tenerife, Canary Islands

Carbon dioxide is one of the first gases to escape the magmatic environment due to its low solubility in basaltic magmas at low pressures. The exsolved CO₂ gas migrates towards the surface through rock fractures and high permeability paths. If an aquifer is located between the magmatic environment and the surface, a fraction of the CO₂ emitted is dissolved in the aquifer. In this paper, an estimation of the water mass balance and the CO₂ budget in Las Cañadas aquifer, Tenerife, Canary Islands, is presented. Magmatic CO₂ is transported by groundwater and discharged through man-made sub-horizontal drains or galleries that exist in this island, and by the flow of groundwater discharged laterally towards other aquifers or to the ocean. In addition, the pCO₂ at the gallery mouth (or entrance) and at the gallery bottom (internal and deepest discharge point where the gallery starts) are calculated and mapped. The total CO₂ advectively transported by groundwater is estimated to range from 143 to 211 t CO₂ d^?1. Considering that the diffuse soil emission of CO₂ for the same area is 437 t d^?1, the diffuse/dissolved CO₂ flux ratio varies between 2 and 3. The high dissolved inorganic carbon content of groundwater explains the ability of this low temperature hydrothermal water to dissolve and transfer magmatic CO₂ at volcanoes, even during quiescence periods.